Which factors determine spring biological bloom in the China Sea?

1. Which factors determine spring biological bloom in the China Sea? Xiaohong Yao Key Laboratory of Marine Environment and Ecology (Ministry of Education), Ocean University of China, Qingdao, 266100, P.R. China 2012.5.10, SOLAS OPEN SCIENCE CONFERENCE

2. Objectives • 1) In the China Sea,which factors determine spring biological bloom (not always occur)? This is a “yes” or “no” question • 2) In the China Sea,which factors enhance spring biological bloom? This is “how much” question • 3) Roles of Asian dust deposition on spring biological bloom in the China Sea

3. Fertilization incubation experiments in the Yellow Sea in March 2011 Surface sea water Dust and nutrients control 200μm filtering bottles Photo of incubation box, each of bottle is 16 L , recycling sea water is used for controlling temperature

4. Route of incubation experiment in March, 2011 Sea water was collected in the mid of the Yellow sea (red star), then direct to East China sea; Atmospheric deposition, including nature and anthropogenic pollutants, was reported to be the major source of nutrients in the Yellow sea. Initial nutrients in sea water: NO3-=1.05 umol/L; NH4+=0.31 umol/L; PO43-=0.15 umol/L;NO2-=0.09 umol/L.

5. Nutrients added in incubation experiment in March, 2011 20 mg/L dust contains0.14 umol/L Fe (total, Fe2+ could be much less than 2 nmol/L)+ 0.005 umol/L PO43-+ (0.14 umol/L NO3-+0.08 umol/L NH4+); Chemical composition of Rainwater was not measured.

6. What determined spring biogenic bloom in the Yellow Sea? A weak biogenic bloom was observed at A2 station from satellite data; Much strong biogenic bloom occurred in the control incubation experiment ; Temperature and PAR (photosynthetically active radiation) were likely the most important limitation factors for biogenic bloom.

7. What can enhance spring biogenic bloom? 1) Doubling NO3- in sea water doubles the concentration of CHLA; 2) Added 20 mg/L dust to sea water increased the concentration of CHLA by about 30% relative to the control; 3) Bio-availability Nitrogen in Dust experiment was only 1/10 of that in NO3- experiment; 4) What caused high efficiency in dust fertilization experiment? In Dust and NO3- fertilization incubation experiments, CHLA was statistically higher than in the controlexperiment A net increase of CHLA in dust experimentrelative to the control was 1/3 of that in NO3-experiment

8. Can Fe, P, Fe+P and rainwater enhance spring biogenic bloom? In Fe, P, (Fe+P) and Rain water fertilization incubation experiments, CHLA was higher than that in the control during the most of experiment times; However, the difference was not statistically significant; More experiments might be needed.

9. Why dust has a high efficiency?-Nutrients in dust fertilization experiment Dust increased concentration of NH4+; Dust decreased PO43- at the initial stage, then released; Minor influences on NO3- and NO2- too much; Overall, unexpected increase of NH4+ relative to NH4+ in sea water; is high efficiency of dust associated with NH4+ input? Fe2+ was not measured in this study

10. Nutrition in NO3- and PO43- fertilization experiment Only about 50% of added NO3- and PO43- were detected in experiments; Reverse daily variations of NH4+ between the control and the NO3- experiment; More NH4+ was released in the NO3- and PO43- experiment than in the control. Daily variations of NH4+ implied: grew and degrade, then grew and degrade… NO3- and NH4+ were used to synthesize organic, then decomposed into NH4+, NH4+ was further used to synthesize organic, then decomposed into NH4+ …

11. Nutrients in rain water fertilization experiment Rainwater did not add the detectable amount of PO43-; Added rainwater increased N by 50%; When considered only 50% of added nutrients can be detected, N added by rainwater could be close to that in NO3- fertilization experiment ; then why low CHLA? NO3- could be partially converted to NH4+? and vice verse?  NO3-  NH4+ ?

12. Experiment in the East China Sea in summer <0.2 um CHLA 2-20 um CHLA >20 um CHLA Total CHLA No bloom for the control andno synthesized effect by Dust Much low concentration of CHLA, only three days for CHLA reaching the maximum. N limitation; not limited by Fe, P and Fe+P (not shown)

13. Conclusion • 1) Temperature and PAR were likely the most important limitation factors for biogenic bloom in the Yellow sea; • 2) Since the ratio of N/P is less than 10 at the ocean zone, the concentration of chlorophyll-a was very sensitive to the external input of N; the concentration also increased with increasing external input of P, but not statistically significant; • 3) N in Dust fertilization experiment was only 1/10 of that in NO3- fertilization experiment, but the net increase of CHLA in the former experiment relative to the control was 1/3 of that in the later experiment; Does this imply that any unknown X could enhance bloom? • 4) In the rainwater fertilization experiment, N increased by about 100%. However, relative to the control, no significant increase of the concentration of chlorophyll-a was observed. Again, Does this imply any unknown X limitation? X appeared to be absent in rainwater and it seems to play a key role for the use of NH4+.

14. Acknowledgement • This study is a team workby my colleagues and students, they are Prof. Huiwang Gao, Jinhui, Shi, Jianhua Qi, students include Tianran Zhang, YangFan, Ying Liu,…

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16. SERIES SEEDS SEEDS II IronEx I , II EisenEx SOIREE SOFeX In situ Fe fertilizer experiments in N.Pac SAGE

17. Most of areas in China Sea is subject to EOZ HNLC China US EOZ LNLC LNLC Surface Chl.a concentration Biological bloom in the China Sea occurred frequently in spring, but not yet well understand; the process could provide a clue to understand dynamics of carbon transfer in the China sea. EOZ: Eutrophic Ocean Zone; HNLC:High-Nutrient Low-Chlorophyll; LNLC:Low -Nutrient Low-Chlorophyll